Whey, a naturally occuring substance, is the serum or watery part of milk which is separated from the curds in the process of making cheese. Dried whey is comprised of about 13% protein and 73% lactose, and the balance inorganic salts. One of the uses of whey in commerce is to ferment it and incorporate it into bakery products, where it acts as a mycostatic agent, thus enabling the products to have substantially longer shelf lives than would otherwise be possible. It has been determined that the active mycostatic agent in whey is propionic acid which is produced as a consequence of the fermentation process.
Suggested bacteria for fermentation, as disclosed in U.S. Pat. No. 1,910,130, include Bacterium acidi-propionici. In previously described processes producing fermented whey, it was desirable to sterilize the whey and to ferment it with a known non-pathogenic culture in order to keep out pathogens, and control the product quality and specifications. One of the steps in the process of fermentation is the sterilization of the whey substrate, which must be done without adversely effecting the subsequent fermentation. Sterilization is necessary in order to kill any residual organisms in the whey prior to introducing the organism for fermentation.
Further, to produce the desired calcium propionate or other divalent metallic ion (M.sup.++) propionate product a difficult to handle and sterilize Ca(OH).sub.2 /NaOH or M(OH).sub.2 /NaOH slurry system was needed for pH control. Therefore, sterile NaOH was used for pH control producing the less desirable sodium propionate. In the improved two-stage sequential fermentation described herein, calcium or other divalent metallic ion is introduced by pre fermenting pasteurized whey with a galactose and glucose utilizing lactic acid-producing bacterial culture or mixture of bacterial cultures and controlling the pH with Ca(OH).sub.2 or M(OH).sub.2. This fermented whey, containing high concentrations of Ca-lactate or M-lactate and no residual reducing sugars, is then sterilized and fermented with a pure culture of propionic acid-producing bacterium to produce high concentrations of calcium propionate or other divalent metallic ion propionates.